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Atualmente, fontes de luz polarizada encontram diversas aplicações em dispositivos optoeletrônicos, “displays”, em testes de tensões em peças mecânicas e até em estudos de mineralogia. Uma das principais necessidades é determinar o estado de polarização (linear, circular, elíptico, ou uma sobreposição destes) do feixe luminoso. Para este fim, aplicamos neste trabalho a técnica de Elipsometria de Emissão para investigar os estados de polarização de diferentes fontes de luz. Esta técnica está baseada na teoria de Stokes e os tipos de polarização estão correlacionados aos parâmetros de Stokes. Realizamos medidas em feixes de luz proveniente de um LASER polarizado, um LASER polarizado passando por um defasador quarto de onda a ± 45° (polarização circular), um LED despolarizado e, esse mesmo LED, com sua luz refletida sobre uma placa de vidro em diversos ângulos e inclusive no ângulo de Brewster. A montagem experimental é composta de um defasador quarto de onda, um polarizador linear e um detector de luz. Os resultados obtidos apresentaram um desvio de aproximadamente 1% em relação à polarização conhecida das fontes de luz. Desta maneira, foi possível constatar que a técnica de Elipsometria de Emissão pode ser aplicada para se determinar a polarização da luz proveniente de fontes luminosas em geral.

A systematic study of the application of self-assembly monolayers (SAMs) onto electron and hole transporting layers for perovskite solar cells (PSCs) stability is reported. Cs0.05FA0.83MA0.17Pb(I0.87Br0.13)3 (FMC) perovskite films were deposited onto tin oxide (SnO2) and nickel oxide (NiOx) layers that were functionalized with ethylphosphonic acid (EPA) and 4-bromobenzoic acid (BBA) SAMs. X-ray diffractometry measurements were performed on these films shortly after they were deposited. The diffractograms agree with the positions reported in the literature for the crystal structure of the FMC. The results show that the deposition of SAMs on the metal oxide layers yields positive improvements in the FMC film stability and in the device stability when using FMC as the active layer. The work shows that by adopting SAMs, the long-term stability of PSCs cells under accelerated test conditions can be enhanced, and this provides one step on the way to making this technology a commercial reality.

In this work we have studied the emissions from luminescent polymeric blends, aiming to obtain a white emission. Two of the materials, a polyfluorene derivative matrix poly(9,9-dihexyl-2,7-fluorene) (LaPPS 10, labeled as L10) and a polyvinylene-derivative guest (poly[(9,9-dihexyl-9H-fluorene-2,7-diyl)-1,2-ethenediyl-1,4-phenylene-1,2-ethenediyl] (LaPPS 16—L16), have not been extensively studied. The L10 was used as a matrix (host) and the L16 as a dopant (guest). A commercial polyvinylene (MDMO-PPV) was also used as a dopant. In order to achieve the white emission, it is necessary to control the energy transfer among the components of the blend. The emissions of solutions were analyzed, varying the concentration of the materials. From that, solutions of polymeric blends of L10:L16 (at different ratios) were spincoated, forming solid state films. The emission of these binary blend films were monitored as a function of the guest concentration. Therefore, in order to cover the red region of the visible spectrum, MDMO-PPV was added to the initial blend, forming a ternary blend (L10:L16:MDMO-PPV). The emissions of these blend films were studied, varying the concentration of the MDMO-PPV. Using the optimal results for the material ratios of these ternary blends, aiming for the white emission, electroluminescent devices were produced and the electroluminescence was studied. A whitish emission was obtained with the 97.5:0.5:2.0 blend, leading to the CIE coordinates 0.31:0.36.

This study analyzed the interfaces between poly(3-hexylthiophene) (P3HT) on an Au substrate (Au/P3HT) and on Au coated with poly(3,4-ethyldioxythiophene) doped with poly(4-styrenesulfonate) (Au/PEDOT:PSS/P3HT). The different morphologies on the nanostructured Au surface were obtained by applying cyclic potentials using cyclic voltammetry to produce different interfaces in the two systems studied. Under atomic force microscopy (AFM), the number of potential activation cycles was found to produce different roughnesses on the surfaces of the Au electrodes. The interfaces formed were examined by electrochemical impedance spectroscopy (EIS) to identify charge transfer processes for the different segments of the P3HT. The systems were characterized optically by measuring photoluminescence (PL), emission decay time and photoluminescence quantum yield (PLQY). It was observed that the differences in the surface morphologies of the substrates significantly influenced the electrical and optical properties of the P3HT at the interfaces.

Mixtures of luminescence downshifting (LDS) materials has been used to increase the efficiency of poly(3-hexylthiophene-2,5-diyl):phenyl-C61-butyric acid methyl ester (P3HT:PC61BM) bulk heterojunction solar cell. This layers convert more energetic photons to lower energies that are better matched with wavelength peak of the external quantum efficiency (EQE) of a P3HT:PC61BM solar cell. Experimental studies were used to optimise the optical properties of LDS layers including the maximum of absorbance and the photoluminescence quantum yield (PLQY). To provide the significant improvements, combinations of LDS mixtures were prepared to provide the greatest absorption and PLQY. The approach is shown to simultaneously improve the photocurrent and increase the lifetime of the device by absorbing UV light. By optimising the optical properties of the LDS mixture, a relative increase of about 20% in the photocurrent density produced by the P3HT:PCBM cell could be achieved, which to our knowledge is one of the most significant reported for OPVs.

The application of luminescent down shifting (LDS) layers as alternative UV filters for CH 3 NH 3 PbI 3(1-x) Cl 3x perovskite solar cell (PSC) devices is reported. A combination of photo-absorption measurements and of device decay measurements during light soaking are used to verify the stability. The application of a UV filter or LDS layer was able to significantly retard photo-induced degradation with ∼18% drop in device power conversion efficiency (PCE) observed over 30 h for non-encapsulated devices, which is compared to ∼97% for an un-filtered device, also without encapsulation. Whilst the PCE of the PSC device decreases with the application of the LDS layer, the drop is not as significant as when a commercial UV filter is used. Considering that UV filters will be essential for the commercialization of PSCs, the work provides evidence that the LDS layer can act as an alternative UV filter in PSCs and can limit the drop in PCE that can be expected from the inclusion of a UV filter, thus providing an added benefit over commercial UV filters.

A systematic study of luminescence from blends made of poly (9, 9-dioctylfluorene-2, 7-diyl) (PFO) and poly (3-octylthiophene-2, 5-diyl) (P3OT), and its photophysics was carried out. Acceptor concentration influence and sample preparation conditions was analyzed, particularly regarding the solvent, in order to control emission through the entire visible spectrum, and to understand the physical processes involved. An additional emission band observed in PFO:P3OT films with low concentration of P3OT was studied through confocal luminescence microscopy and was attributed to a decrease of energy transfer between P3OT molecules leading to an emission through chains with smaller conjugation length. The extra emission was also separated from the others by Time Resolved Emission Spectroscopy due to the fact that its lifetime is longer than those of the other emissions. Balance control of the emission through PFO (blue), low conjugation chains of P3OT (green) and P3OT aggregates (red) was possible changing the solvent and the way to prepare samples, that causes a greater or lesser amount of β phase in PFO. The study of the energy processes involved was also performed.

In the present paper it is demonstrated that the bound electronic states of multiple quantum wells structures may be calculated very efficiently by expanding their eigenstates in terms of the eigenfunctions of a particle in a box. The bound states of single and multiple symmetric or nonsymmetric wells are calculated within the single-band effective mass approximation. A comparison is then made between the results obtained for simple cases with exact calculations. We also apply our approach to a GaAs/AlGaAs multiple quantum well structure composed of forty periods each one with seven quantum wells. The method may be very useful to design narrow band quantum cascade photodetectors to work without applied bias in a photovoltaic mode. With the presented method the effects of a electric field may also be easily included which is very important if one desires study quantum well structures for application to the development of quantum cascade lasers. The advantages of the method are also presented.

In this work we studied the optical properties of poly(p-phenylene vinylene) (PPV) produced by the thermal con- version of a precursor polymer blended with a synthetic dye (Reactive Black 5). The production of PPV by this method decreases the overall time and cost of the process. We observed that the introduction of the dye resulted in an additional absorbance band near 550-700 nm, which can be beneficial to the photon harvesting capacity of the polymer if it is used as the donor material in a photovoltaic device. We studied how the optical and structures properties of this blend change when different quantities of TiO2 nanoparticles are introduced. For that, thin films were produced by the cast deposition of pre- PPV:dye:TiO2. The scanning electronic microscopic images showed that the inorganic semiconductor form large agglomer- ates of approximately 200 nm, indicating a very rough surface where the dye can be adsorbed. The analysis of photolumi- nescence and Raman peaks indicated a reduction of the mean conjugation length of the polymer chains in the presence of TiO2 nanoparticles.

In this work, poly (3-methylthiophene) (P3MT) and poly (3-octylthiophene) (P3OT) films were synthesized electrochemically in non-aqueous media through the oxidation of the monomers, (3-methylthiophene and 3-octylthiophene), using a standard three-electrode cell in acetonitrile with 0.100 mol L-1 LiClO4. The polymeric thin films were deposited on platinum plates for optimal quality control of the process. It was observed that the material as-prepared for the anodic electropolymerization undergoes a natural process of de-protonation as a function of time. Moreover, the partial dedoped form, obtained in NH4OH solution, presents a good chemically stabilite form but, when radiated with blue light again becomes unstable. Films obtained by these methods have been characterized by cyclic voltammetry, Raman and photoluminescence spectroscopy. Both Raman and photoluminescence (PL) spectra results led to the characterization of two structures (pristine and non-pristine forms of thiophene rings) which formed the P3MT and P3OT polymer chain. These results were associated with the stabilization of pristine chains and mixed chains (non-pristine structures), radical cation and dication forms, in the polymeric film. Their bands in the Raman and PL spectra are wide and asymmetric and their adjustments by Gaussian functions were necessary, indicating that there are three distinct contributions to the vibration and two to the emission spectra in the formed polymeric material.

In this work, poly(3-hexylthiophene) (P3HT) film was synthesized electrochemically in non-aqueous media through the oxidation of the 3-hexylthiophene monomer using a standard three-electrode cell in acetonitrile with 0.100 mol L−1 LiClO4. The polymeric thick film was deposited on platinum plates for best quality control of the process. Cyclic voltammetry of this material showed two bands of oxidation and two bands of reduction attributed to radical cation and dication segments in the polymer chain. These were characterized by reflectance and Raman spectra, of the reduced (chemically de-doped) and oxidized (electrochemically doped) films. The generated film was subjected to anodic potentials of 1.00 and 1.45 V and characterized by an in situ Raman technique, which indicated the stabilization of the radical cation segments. In addition Raman ex situ spectra of as-prepared film was obtained. The increase in the irradiation time of the sample was enough to alter the nature of the constituent species of the oxidized film, preferably favoring the aromatic chains, together with the dication segments. Photoluminescence spectra showed a larger contribution of dication than radical cation segments for the chemically de-doped sample and under this condition showed good stability, even with variation in laser power. SEM images of P3HT film with indication of the thickness and spherical shape of the sample studied were obtained. Aided by these data it was possible to verify the Stokes shift and ionization potential (I p), electron affinity (E.A.) and energy gap (E g) parameters.

In this work we report on a comparison of some theoretical models usually used to fit the dependence on temperature of the fundamental energy gap of semiconductor materials. We used in our investigations the theoretical models of Vi˜ na, P¨ assler-p and P¨ assler-r to fit several sets of experimental data, available in the literature for the energy gap of GaAs in the temperature range from 12 to 974 K. Performing several fittings for different values of the upper limit of the analyzed temperature range (T max), we were able to follow in a systematic way the evolution of the fitting parameters up to the limit of high temperatures and make a comparison between the zero-point values obtained from the different models by extrapolating the linear dependence of the gaps at high T to T = 0 K and that determined by the dependence of the gap on isotope mass. Using experimental data measured by absorption spectroscopy, we observed the non-linear behavior of Eg(T) of GaAs for T > QD.

We present a comparative study carried out on the optical and electrical characteristics of undoped and Te doped AlGaAsSb/AlAsSb Bragg mirrors with 6.5 pairs of layers and bulk undoped and Te doped AlGaAsSb epilayers alloys lattice matched on InP, grown by molecular beam epitaxy, using SIMS, photoluminescence, reflectivity and IxV techniques. The temperature dependence of PL transitions observed in the Bragg mirrors are similar to that observed in bulk samples and associated with the donor and acceptor recombinations in alloys with electrostatic potential fluctuations described by quasi-donor-acceptor-pair (QDAP) models. We verified by SIMS the presence of a macro fluctuation in the Te profile concentrations in the growth direction of the doped Bragg mirror. The influence of doping, alloy and macrofluctuation of incorporated Te on the optical and electrical properties of doped Bragg mirror is analyzed. The AlGaAs/AlAsSb seems a very attractive option for VCSEL technology.

A detailed study of the photoluminescence properties in undoped and Te-doped AlGaAsSb alloys lattice matched to InP is presented. Photoluminescent temperature and excitation intensity dependences are employed to discuss the origin of the dominant transition and the influence of the presence of Al and Te on the fluctuation of the electrostatic potential in the epitaxial layers. The behavior of PL dominant transitions is associated with the quasi-donor-acceptor-pair (QDAP) model at a low temperature interval. The temperature dependence of photoluminescence intensities showed characteristics similar to those observed for amorphous semiconductors and disordered superlattices. The presence of two V elements, or the presence of Sb in the ternary and quaternary (III)-III-V-V alloys, causes a reduction in photoluminescence intensity temperature dependence, when compared to (III)-III-III-V alloys.

International audience; This work examines the photodegradation of poly(3-octylthiophene) (P3OT) by UV-irradiation at 405 nm under vacuum and as a function of temperature (300 and 10 K). Two different P3OT films were studied. The first one was electrochemically synthesized on platinum plate and chemically reduced in a basic medium (P3OT-E) whereas the second one, chemically synthesized was spread out on glass by casting process from polymer previously dissolved in chloroform (P3OT-Q). After 200 s under UV illumination, the photoluminescence (PL) spectra observed on the P3OT-E samples showed an unexpected increase of some eight times in the emission intensity. In contrast, the PL spectra of P3OT-Q, subjected to the same temperature, pressure and photoirradiation time, showed a drop of to around half the initial signal intensity. Similarly experiments were performed at low temperature 10 K. In this temperature condition, PL spectra of P3OT-E and P3OT-Q obtained under photoirradiation, presented similar decreases of the intensity of their fluorescence. In order to explain these different results, Raman spectroscopy studies had been performed, and it was been possible to follow the formation of C=O group on the side alkyl chain after 200 min of irradiation. From the results obtained, we proposed a mechanism to explain the unexpected intensification of the PL emission signal for P3OT-E at 300 K. This mechanism was based on the destabilization of the charge transfer complex between the radical cations in P3OT-E and the residual dioxygen.

In this study, we observed significant differences in the electrical and optical properties of polymer films electrochemically synthesized from two 3-alkylthiophene monomers on platinum wires in 0.100 mol L−1 LiClO4/acetonitrile (ACN) or Et4NBF4/ACN, when compared to the following homopolymer films: poly(3-methylthiophene) (P3MT), poly(3-hexylthiophene) (P3HT) and poly(3-octylthiophene) (P3OT), prepared under the same conditions. Electrical impedance spectroscopy was used to assess the resistive and capacitive properties of the polymer films [P3MT and P3HT—CP3(MT-HT); P3MT and P3OT—CP3(MT-OT); P3HT and P3OT—CP3(HT-OT)] at overpotentials determined beforehand by Cyclic Voltammetry. The films synthesized in LiClO4/ACN with the lowest charge transfer resistance values were CP3(MT-HT) and CP3(MT-OT), and synthesized in Et4NBF4/ACN, CP3(HT-OT). In terms of their optical properties, the films synthesized in LiClO4/ACN exhibited hypsochromic shift of E g values and a drop in electron affinity values by comparison with homopolymer films and those synthesized in Et4NBF4/ACN. Based on Photoluminescence (PL) Spectroscopy it was possible to identify the contributions of the quinone and aromatic segments characteristic of homopolymers in the films synthesized in Et4NBF4/ACN. For the films synthesized in LiClO4/ACN, it was not possible to perform the same comparison because there was a discrepancy between the bands observed in the PL images of these materials and those of the homopolymers, suggesting the formation of not only blend structures but also copolymer films. Using Raman Spectroscopy it was possible to identify aromatic, radical cation and dication segments and verify the higher stabilization of radical cation and dication segments in resistive films. It was also possible to observe changes in the morphological structures of the films by comparison with the homopolymers, in addition to alterations due to changes in electrolyte during synthesis using scanning electron microscopy.

Luminescence down-shifting (LDS) is used in several photovoltaic technologies aiming to improve the photon conversion efficiency (PCE) of the devices through the increase of the light harvesting in the regions of the electromagnetic spectrum where the EQE of the solar cells is poor. The aim of this work was to produce films of mixtures (blends) of two luminescent materials, dispersed in a poly-methyl methacrylate (PMMA) matrix, hoping to improve their properties both as LDS layer and as UV filter when applied on the clear, external surface of P3HT:PC61BM photovoltaic devices. The best results led to an increment of 7.4% in the PCE of the devices, and a six fold enhancement in their half-life (T 50%). This study indicates that multidye LDS layers with optimized optical properties can lead to an effective improvement in the performance and operational stability of OPVs.

The mechanism for low-temperature photoluminescence (PL) emissions in GaAsSb/AlGaAs and GaAsSbN/GaAs strained-layer single quantum wells (SQWs), grown by molecular-beam epitaxy, is studied in detail, using PL spectroscopy as a function of temperature and excitation intensity. In all samples, the PL peak energy as well as the full width at half maximum (FWHM), as a function of temperature, present anomalous behaviors, i:e., the PL peak energy shows a successive red/blue/redshift (S-shaped behavior) and the FWHM shows a successive blue/red/blueshift (“inverted S-shaped curve”) with increasing temperature. At sufficiently low excitation intensity and in a narrow temperature interval (50 ‐ 80 K), the nitrogen-containing samples present two clear competitive PL peaks. The low-energy PL mechanism (8 ‐ 80 K) is dominated by localized PL transitions, while the high-energy PL mechanism is dominated by the ground state (e1-hh1) PL transition. Additionally, these PL peaks show different temperature dependence with the low-energy PL peak, showing a stronger redshift than the high-energy PL peak. A competition process between localized and delocalized excitons is used to discuss these PL properties.

In this work we describe the processing of poly(styrene sulphonate) films (PSS) doped with neodymium (Nd). Optical density measurements in the UV-Vis-NIR region show the typical bands observed for neodymium chloride (NdCl3) in solution. In the case of films, the intensity ratio between the peaks at 800 nm (4I9/2 -> 4F5/2 + ²H7/2) and 580 nm (4I9/2 -> 4G5/2 + ²G7/2) is equal to 0.83. Infrared spectra present an enhancement in the absorption region of aromatic rings. Site selective luminescence spectroscopy shows that the incorporation of Nd introduces a hipsochromic shift and a line shape definition in UV luminescence compared to PSS film, decreasing the interaction between aromatic groups. In addition, the film exhibits an intense radiative transition at 1061 nm (4F3/2->4I11/2), comparable to the one present in crystalline materials doped with Nd.

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:01:22Z No. of bitstreams: 1 S0103-97332004000400022.pdf: 163059 bytes, checksum: cd009132f334dd2586e6a14554357af3 (MD5) Made available in DSpace on 2013-08-22T19:01:22Z (GMT). No. of bitstreams: 1 S0103-97332004000400022.pdf: 163059 bytes, checksum: cd009132f334dd2586e6a14554357af3 (MD5) Previous issue date: 2004-06-01 Made available in DSpace on 2013-09-30T20:01:20Z (GMT). No. of bitstreams: 2 S0103-97332004000400022.pdf: 163059 bytes, checksum: cd009132f334dd2586e6a14554357af3 (MD5) S0103-97332004000400022.pdf.txt: 13097 bytes, checksum: 41e6751a54fdae567496162132c6b3bb (MD5) Previous issue date: 2004-06-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:15:41Z No. of bitstreams: 2 S0103-97332004000400022.pdf: 163059 bytes, checksum: cd009132f334dd2586e6a14554357af3 (MD5) S0103-97332004000400022.pdf.txt: 13097 bytes, checksum: 41e6751a54fdae567496162132c6b3bb (MD5) Made available in DSpace on 2014-05-20T15:15:41Z (GMT). No. of bitstreams: 2 S0103-97332004000400022.pdf: 163059 bytes, checksum: cd009132f334dd2586e6a14554357af3 (MD5) S0103-97332004000400022.pdf.txt: 13097 bytes, checksum: 41e6751a54fdae567496162132c6b3bb (MD5) Previous issue date: 2004-06-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação para o Desenvolvimento da UNESP (FUNDUNESP) In this work we investigated the optical and structural properties of GaAs/GaInP quantum wells (QW) grown by Chemical Beam Epitaxy (CBE). The samples were characterized by photoluminescence (PL), photoluminescence excitation (PLE) and transmission electron microscopy (TEM). Simulations of the quantum well potential profiles, using the Van de Walle-Martin model, supplemented by our experimental results, allowed us to associate the interface properties with the growth procedures. We concluded that a thin GaP layer grown at the interface improves its quality and also that the observed broad emission band in the PL spectrum is related to quaternary Ga1-xIn xAs1-yPy. Universidade Estadual Paulista - UNESP Departamento de Física UNICAMP Instituto de Física Gleb Wathagin Laboratório Nacional de Luz Sincroton - LNLS Universidade Estadual Paulista - UNESP Departamento de Física

Submitted by Guilherme Lemeszenski (guilherme@nead.unesp.br) on 2013-08-22T19:01:19Z No. of bitstreams: 1 S0103-97332002000200017.pdf: 180353 bytes, checksum: 2194adc05325048b8fbc21a686c29502 (MD5) Made available in DSpace on 2013-08-22T19:01:19Z (GMT). No. of bitstreams: 1 S0103-97332002000200017.pdf: 180353 bytes, checksum: 2194adc05325048b8fbc21a686c29502 (MD5) Previous issue date: 2002-06-01 Made available in DSpace on 2013-09-30T20:01:14Z (GMT). No. of bitstreams: 2 S0103-97332002000200017.pdf: 180353 bytes, checksum: 2194adc05325048b8fbc21a686c29502 (MD5) S0103-97332002000200017.pdf.txt: 13279 bytes, checksum: 38c5a5f948ee92fd54c3dc16a3694924 (MD5) Previous issue date: 2002-06-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:15:39Z No. of bitstreams: 2 S0103-97332002000200017.pdf: 180353 bytes, checksum: 2194adc05325048b8fbc21a686c29502 (MD5) S0103-97332002000200017.pdf.txt: 13279 bytes, checksum: 38c5a5f948ee92fd54c3dc16a3694924 (MD5) Made available in DSpace on 2014-05-20T15:15:39Z (GMT). No. of bitstreams: 2 S0103-97332002000200017.pdf: 180353 bytes, checksum: 2194adc05325048b8fbc21a686c29502 (MD5) S0103-97332002000200017.pdf.txt: 13279 bytes, checksum: 38c5a5f948ee92fd54c3dc16a3694924 (MD5) Previous issue date: 2002-06-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Photoluminescence (PL) and excitation PL measurements have been performed at different temperatures in a number of lattice-matched GaAs/In0.49Ga0.51P quantum wells, where the uctuations of the potential energy are comparable with the thermal energy of the photocreated carriers. Two samples with different well widths allow to observe a series of anomalous e ects in their optical response. The observed effects are related to the disorder in the interface, characterizing uctuations in the confinement potential energy. It is proposed that the carrier relaxation processes occur either at the local minima or at the absolute minimum of the confinement potential, depending on the ratio of the thermal energy and the magnitude of the potential fluctuations. Universidade Estadual de Campinas Instituto de Física 'Gleb Wataghin' Laboratório Nacional de Luz Síncrotron Universidade de São Paulo Instituto de Física Universidade Estadual Paulista Departamento de Física Universidade Estadual Paulista Departamento de Física

Orientador: Eliermes Arraes de Meneses Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Não informado Abstract: Not informed. Doutorado Física Doutor em Ciências

Orientador: Eliermes Arraes Meneses Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: São investigadas as propriedades elétricas e óticas na região excitônica do InP utilizando as técnicas de efeito Hall e fotoluminescência a baixas temperaturas, respectivamente. As amostras analisadas foram crescidas pela técnica de CBE (epitaxia por feixe químico), cujo sistema foi recentemente instalado no IFGW/Unicamp. Os espectros de fotoluminescência caracterizam-se pelas linhas excitônicas intensas nas amostras sem dopagem, e são bem distintos para amostras com diferentes níveis de dopagem de Silício. Uma linha de luminescência situada em 1 ,389 eV é observada nas amostras dopadas, e é atribuída à transição radiativa D0si-A0si. A energia de ligação do Si como aceitador no InP é estimada em 28 meV. Outra linha, em 1 ,401 eV, se torna bastante evidente em amostras onde houve incorporação de impurezas de Arsênio. Com base na sua posição em energia, forma de linha, e correlação com a presença de As, é sugerido que esse pico esteja relacionado à recombinação de éxcitons ligados a "traps" isoeletrônicos, gerados por impurezas de As substituindo sítios do P. A formação desse estado ligado pode estar sendo assistida pela distorção da rede causada pela dopagem com Silício Abstract: Not informed Mestrado Física Mestre em Física

O rapido progresso das tecnicas de crescimento de materiais semicondutores possibilitou a fabricacao de uma serie de novos dispositivos que contribuiram para o desenvolvimento da nanotecnologia. A confeccao de heteroestruturas semicondutoras de alta qualidade permite a obtencao de novos efeitos baseados nas propriedades quânticas desses sistemas, os quais despertam grande interesse tecnologico, especialmente nos setores opto-eletronico e de telecomunicacoes. Neste trabalho sao discutidos alguns conceitos basicos relacionados a uma dessas heteroestruturas: o Poco Quântico Duplo Acoplado (PQDA). A deducao da expressao para a determinacao dos niveis de energia de PQDAs e apresentada em detalhes. Os resultados obtidos atraves desta expressao sao comparados com resultados experimentais obtidos atraves da tecnica de fotoluminescencia (PL), complementando o trabalho.

In this paper we investigate the optical properties of thin films produced through the layer-by-layer (LbL) technique with a poly (p-phenylene vinylene) (PPV) precursor and the Congo Red (CR) azodye. Some significant changes are observed when the PPV/CR film is irradiated with polarized laser. An increase of about 10 times in the PPV emission intensity was observed, with an irradiation time of 100 min. Photoinduced birefringence measurements revealed that a high birefringence was produced in the region of the film submitted to photo-irradiation, while a photobleaching phenomenon was observed in the same region. However, such phenomena were not detected in measurements performed at low temperatures. The results indicate that a degradation process of the CR molecules is occurring with photo-irradiation, and the changes observed in the photoluminescence spectra are correlated with the combined effects of degradation and energy transfer between the PPV light-emitting conjugated segments and CR azochromophores.

In this work the P3MT was synthesized electrochemically on transparent conductive substrates of fluorine tin oxide (FTO) using the electrolyte Et 4 NBF 4 in acetonitrile. To dedope the material, the samples were reduced electrochemically and chemically (in NH 4 OH solution). The films were characterized by electron paramagnetic resonance spectroscopy (EPR) and infrared spectroscopy (FTIR) and their optical properties examined by ultraviolet–visible absorption spectroscopy (UV–vis) and photoluminescence (PL). The FTIR spectra show the characteristic features of P3MT and, together with the results of EPR, allowed to evaluate the charge carriers and to identify benzene and quinones in the formation of chains. The UV–vis absorption spectra helped to obtain the average gap energy of P3MT and presented the π – π * transition band and a bipolaron band. In the PL spectra, with variation of excitation power and temperature, studies were performed through the fit with Gaussian functions, given the strong probability of the existence of two distinct contributions in the formation of the emission spectra. These two contributions were assigned to the emission of mixed chains (Gaussian centered at higher energy) and emission of benzenoid chains (Gaussian of lower energy) in the formed polymeric material.

O biodiesel é produzido a partir de fontes renováveis, podendo ser obtido a partir de óleos vegetais, gorduras animais e graxas residuais. Esse biocombustível é formado por ésteres de ácidos graxos facilmente degradados através do contato com oxigênio, variações de temperatura, contato com metais ou contaminantes. Assim, o processo de degradação oxidativa ocasionado pela reação radicalar irreversível é uma das grandes preocupações sobre esse biocombustível. Na primeira parte do trabalho investigou-se o processo oxidativo do biodiesel a partir da Ressonância Paramagnética Eletrônica (RPE), juntamente com a técnica de aprisionamento de spin (spin trapping), usando a armadilha de spin PBN, acompanhando a formação de radicais livres em amostras de biodiesel e diferentes matérias-primas (soja, milho e canola), com antioxidantes sintéticos (TBHQ, BHT e BHA) e extratos naturais (alecrim, orégano e manjericão). Através dos espectros obtidos por RPE percebeu-se a existência de um antioxidante adequado para cada biodiesel obtido por causa das diferentes matérias-primas, uma vez que o extrato de orégano mostrou melhor desempenho nas amostras de biodiesel de canola e soja, enquanto o extrato de alecrim apresentou maior eficiência no biodiesel de milho. O radical OH foi caracterizado a partir das simulações computacionais dos espectros de RPE. Assim, a técnica de RPE, juntamente com a técnica de spin trapping, mostrou-se eficiente na avaliação da atuação de moléculas com propriedades antioxidantes no processo degradativo do biodiesel. Na segunda parte do trabalho foi investigado o processo de degradação do biodiesel comercial, a partir da espectroscopia de Ressonância Magnética Nuclear de prótons (1H RMN), observando os sinais dos hidrogênios olefínicos, alílicos e bisalílicos das ligações químicas. As amostras foram analisadas na presença dos íons metálicos Fe3+ e Cu2+ e com extrato de alecrim. Observou-se que os metais catalisaram a reação de oxidação, enquanto o extrato de alecrim retardou o processo degradativo. As análises de RMN mostraram quedas nas intensidades dos sinais dos hidrogênios olefínicos, alílicos e bisalílicos e, foi possível realizar a identificação dos produtos de oxidação (aldeídos). A técnica de RMN, mostrou-se capaz de fornecer informações relevantes quanto ao processo degradativo do biodiesel a partir da detecção da formação de co-produtos da reação e das mudanças nas intensidades dos sinais dos hidrogênios alílicos, olefínicos e bisalílicos. Na terceira parte do trabalho foi investigada a termo-oxidação do biodiesel usando a 1H RMN. Dois conjuntos de biodiesel foram analisados, um grupo foi degradado no equipamento Rancimat a 110 ºC por 8 horas, e o segundo foi degradado em estufa durante 17 dias a 50 ºC. A partir dos espectros foram observadas as variações das intensidades dos hidrogênios olefínicos, alílicos e bisalílicos, obteve-se as proporções dos grupos acil oleico, linoleico, linolênico e saturado, além de observar e caracterizar alguns produtos de oxidação. O biodiesel aquecido a 110 ºC mostrou maior grau de oxidação. As amostras apresentaram aumento nas proporções de saturações e produtos como hidroperóxidos e aldeídos foram detectados. A RMN mostrou-se uma boa técnica alternativa para analisar a degradação do biodiesel. Biodiesel is a renewable fuel. It can be obtained from vegetable oils, animal fats and residual oil. This biofuel is formed by fatty acids esters, easily degraded through contact with oxygen, temperature variations, contact with metals or contaminants. Thus, the process of oxidative degradation caused by the irreversible radical reaction is one of the major concerns about this biofuel. In the first part of the work, the oxidative process of biodiesel was investigated using Electronic Paramagnetic Resonance (EPR), together with the spin trapping technique, using the PBN spin trap, following the formation of free radicals in biodiesel samples from different raw materials (soy, corn and canola), with synthetic antioxidants (TBHQ, BHT and BHA) and natural extracts (rosemary, oregano and basil). Through the spectra obtained by EPR, it was noticed the existence of a suitable antioxidant for each biodiesel obtained from the different raw materials, since the oregano extract showed better performance in the canola and soybean biodiesel samples, while the extract of rosemary showed greater efficiency in the corn biodiesel. The OH radical was characterized in the samples from computer simulations of the EPR spectra. Thus, the EPR proved to be efficient in the performance evaluation of the molecules with antioxidant properties in the biodiesel degradation. In the second part of the work, the degradation process of commercial biodiesel was investigated, using Proton Nuclear Magnetic Resonance (1H NMR) spectroscopy, observing the chemical bonds signals of the olefinic, allylic and bisalilic hydrogens. The samples were analyzed in the presence of Fe3+ and Cu2+ metallic ions and with rosemary extract. It was observed that the metals catalyzed the oxidation reaction, while the rosemary extract delayed the degradative process. The NMR analyses showed decreases in the signal intensities of olefinic, allylic and bisalilic hydrogens, and it was possible to identify oxidation products as aldehydes. The NMR technique was able to provide relevant information regarding the degradative process of biodiesel from the detection of co-products formation and changes in the signals’ intensities of the allylic, olefinic and bisalilic hydrogens. In the third part of the work, the thermo-oxidation of biodiesel was investigated using 1H NMR. Two sets of biodiesels were analyzed, one group was degraded in the Rancimat equipment at 110 ºC for 8 hours, and the second was degraded in an oven for 17 days at 50 ºC. From the spectra, variations in the intensities of olefinic, allylic and bisalilic hydrogens were observed, the proportions of oleic, linoleic, linolenic and saturated acyl groups were obtained, in addition to observing and characterizing some oxidation products. The biodiesel heated at 110 ºC showed a higher degree of oxidation. The samples showed an increase in the proportions of saturations and products such as hydroperoxides and aldehydes were detected. NMR spectroscopy proved to be a good alternative technique to analyze the biodiesel degradation.